The invention relates to a device for learning and practicing a correct hip rotation in all types of sports, in particular a correct hip rotation for the execution of an efficient golf swing.
The significance of the invention will be explained below in terms of golfing, one of the main uses of the device according to the invention. The invention, however, relates generally to all types of sports in which the execution of a correct hip rotation plays an important role, e.g. all throwing disciplines, tennis, baseball, etc. It is not necessary to describe the actual hip motion to be executed or various sport types since the action of the device according to the invention can be easily compared and transferred to each type of sport.
The execution of a correct hip rotation during the golf swing is of appreciable significance for the result of a golf shot, in particular for precision of aim and distance of the shot.
In an optimal stroke motion, the hip axis defined by the pelvic bones moves in a plane which is essentially perpendicular to the longitudinal axis and, slightly inclined in respect to the vertical, axis of the torso. The phases of a stroke motion are schematically represented in FIGS. 4a-4c or better understanding of the object which forms the basis of the invention.
FIG. 4a shows the stance of a golfer with a fully completed backswing, i.e. at the reversal point between backswing and stroke motion. In this position, the hip axis or its protection in a horizontal plane, together with the target line L, which is defined by the golf ball 1 and the hole 3, encompasses an angle of approximately 60.degree. During the swing motion of the golf club 5 toward the golf ball 1, whose first phase is shown in FIG. 4b, the torso rotates around its longitudinal axis 0. At the same time, the hip axis H rotates in a plane E perpendicular to the longitudinal axis 0 of the torso. Naturally, the same is also true for the backswing.
All joint and muscle movements of the body, which produce the speed of the club head--and thereby determine the momentum and the kinetic energy of the club head--and which movement are responsible for the flight direction of the ball, are related to the hip motion and its rotation plane. Only a hip rotation which is matched to the arm, club, and shoulder axis assures the correct, efficient golf swing and prevents the club head from leaving the ideal path, which is disposed in a single plane.
Hence, up to the point when the ball is hit, the hip rotation should lead in relation to the shoulder axis motion and arm/club motion and from that moment to the end of the swing should coincide as much as possible with the arm swing motion and leg motion.
Only by means of such coincidence can it be achieved that the momentum of the club head at the point of impact acts on the golf ball in the correct direction. The projection of the movement direction of the club head at the point of impact in a horizontal plane defines the stroke line, which stroke line is shown in FIGS. 4a-4c by the arrow I. The stroke line I encompasses a definite angle together with the target line L, which is defined by a straight line connecting the hole to be played with the ball. The golfer chooses this angle depending upon relevant factors, such as the ball spin to be imparted, etc. In a "normal, straight shot", this angle is approximately 30.degree. opposite to the rotation direction of the hips during the actual stroke motion.
On the whole, starting from the initial position or addressing position, i.e. in the position in which the club head 5a is situated close to the golf ball 1 and in which the hip axis H is essentially parallel to the target line L, during the backswing the hip axis executes a rotation of up to approximately 60.degree. in a first direction, and during the subsequent actual stroke motion a rotation of up to approximately 180.degree. in a second opposite direction.
Up till now, the only option for learning a correct hip rotation during the golf swing was the process used by golf instructors in which the golf club is held in front of the torso of the player in a position parallel to the hip axis and the correct hip rotation during the swing is explained in this manner. But this is only a method of demonstration which is not practicable during the actual swing to be executed by the player.
The same is true for other sports. There, too, in order to explain a correct hip motion or to demonstrate an incorrect one, the instructor would hold a piece of sports equipment, for example the baseball bat, in the hip axis of the person or athlete.